Multiplex system having channels added at a relay station



`June 3,l 1.947 l... E. THOMPSON MULTIPLEX SYSTEM HAVING CHANNELS ADDED AT A RELAY STATION Filed April 9, 1945.

2 Sheets-Sheet l INVENTOR. LELAND E. THOMPSON BY. )f

o MM

ATTORNEY June 3, 1947- Y l.. E. THOMPSON 2,421,727

MULTIPLEX SYSTEM HAVING CHANNELS ADDED AT RELAY STATlON 2 sheetssmet 2 Filed April `9, 1945 i JNVENToR.

LELAND E. THOMPSON BY f6@ MWL,

ATTORNEY "tively lw frequency, sub-sub carriers.

Patented June 3, 1947 MULTIPLEX SYSTEM HAVING CHANNELS ADDED AT A RELAY STATION Leland E. Thompson, Merchantvlle, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application April 9, 1945, Serial N0. `587,250

-My present invention relates to a multi-channel radiorelaying system such as described in my co-pending application Serial Number 576,453, filed February 6, 1945.

' As described in my co-pending application, several different signaling channels are used to independently amplitude modulate separate, rela- The lower side bands of the modulated sub-sub carriers are filtered out, amplified, combined and used to angle, or more specifically, frequency modulate a common sub-carrier wave having a mean frequencyrof, for example, one megacycle. By way of example, also, six different channels may be used to produce a maximum frequency swing of approximately plus and minus 200 kilocycles in the common, frequency modulated sub-carrier. The frequency modulated sub-carrier, having a mean frequency of one megacycle and a maxi mum frequency swing of plus and minus 200 kiloe cycles, is used to frequency or angle modulate the radiated carrier. The latter may have a mean frequency of, for example, 3000 megacycles. The 3000 megacycle radiated carrier may be swung or frequency modulated a maximum amount of, for example, plus and minus one megacycle by the frequency modulated sub-carrier.

The 3000 megacycle carrier is directively radiated to a distant relaying point for retransmission to a receiving terminal or to still another relaying point. The frequency of retransmission takes place at a frequency differentl than that received such as, fur example, 3010 megacycles.

To effect this frequency transformation at a relaying point or station, the received high frequency carrier having an unmodulated frequency of, say, 3000 megacycles, is heterodyned down to some convenient intermediate frequency such as 30 megacycles. The latter is amplified, limited and subjected to a frequency demodulation, i. e., to discriminator-detector action, in order to reproduce the common frequency modulated subcarrier.l This frequency modulated sub-carrier is further limited and amplied and then used to frequency modulate a new, `locally generated, carrier having a frequency of, for example, 3010 megacycles. The new carrier is directively radiated on to the next point in the relay system.

In such a multi-channel radio relay system, it is desirable, in some cases, to tap in at a relay station in order to add one or more signaling channels for transmittal, along with the channels valready present, on to the next point in the system. One way of accomplishing this is to subject the common frequency modulated sub-carrier to Claims. (Cl. 179415) i a second frequency lclemodulation process soas to reproduce the combined single side band channels originally transmitted. The new channel or intelligence band may then be combined with the output of the second demodulator and the paralleled channels may be `used to frequency `modulate a newly generated, common sub-carrier andthe latter may be employed to frequency modulate a newly `generated radio frequency carrier. This method isobjectionable, for unless elaborate and costly equipment in used to increase linearity of the second frequency demodulator and immediately following modulators, an undesirable amount of cross modulation will be introduced, especially in the event that the process is repeated at a number of repeater or relaying stations.

Y It is, therefore, an `object of my present invention to provide an improved method and improved arrangement of instrumentalities for adding one or more intelligence channels to a through wave at a high frequency relay or repeater station without introducing objectionable distortion or cross modulation.

A further object of my present invention is to `provide simplified equipment at relaying points Aenabling the addition of one or more channels to through waves already carrying one or more intelligence frequency bands.

' `In accordance with one form of my present invention wherein one or more intelligence bands or signals are added at a high frequency relaying at the 'relaying station, to a single demodulation. Waves derived from the demodulation are then heterodyned with an oscillation which has been modulated with one or more signals which are to be added at the relaying point. Waves derived from the heterodyning process are then employed to modulate a locally generated high frequency carrier which is to be transmitted on to the next point in the system. y

`My present invention will be described more specically withthe` aid of the accompanying drawing wherein Fig. 1 illustrates a radio relaying station for relaying a doubly frequency modulated wave and wherein one or moresighaling channels may be added at the relaying station with a minimum of distortion and cross talk, and Fig. 2 is a block diagram of a modified form of a relaying station such as shown in Fig. 1.

Fig. 1 is a radio relaying station especially adapted for relaying a multi-channel doubly frequency modulated Wave such as emitted by the transmitting station of Fig. 1 of my co-pending application Serial Number 576,453, filed February 6, 1945. It differs over the relaying system shown in Fig. 2 of that application in that Fig. 1 herein describes an arrangement in which one or more signaling channels may be added at the relaying point with a minimum f cross modulation and distortion.

As shown in Fig. 1 herein a Wave such as transmitted by the transmitter of my co-pending application or as transmitted by the transmitting antenna of any one of the relaying stations Vof my co-pending applicatiomis received upon antenna 2 provided with a parabolic reiiecto'rdv in order to enhance directive reception. The received waves, which may have a mean frequency of 3000 megacycles, are fed 4through line `6 to apparatus 8 which may include a local `'oscillating a first detector, an intermediate frequency amplifiery and a, limiter. Apparatus 8corresponds to converter- '2, beatingpsoillator 204 and intermediate frequencyfamplier 20S of vmy o o-pending- ,applicatiom The heterodyned outputof apparatus 8 may be, for exam-ple, an intermediate frequencywave having a mean frequency of mcgacycles anda deviation of plus and minus one megacycle. v y

y Thiswaveoutput is fed Vthrough line luto a first frequency demodulator or discriminator-detector I2 correspondingto 2GB of Fig. 2 of my cci-pending application. 'Ihe outputio'f apparatus lf2` maybe a wave having a mean frequency of one `megacycle andjfrequencyrmodulated or swung plus and minus ,200kilocycles by the 'signaling channels when allfof them areinstantaneously Qfsuchphase as, toA produce additive frequency modulations in 'the common one megacycle sub- Garrerapreangin lirle M- Fart Ao i the output of the first demodulator I2 appearingin line'lll islfed through line I6 4to a second demodulatorjZp and then to channeling equipment or lters 22'for reproducing one or more ofthe original signaling currents. The seconddeinodulator 2\ c'o rresponds,to the second discriminatorfdetector 312 of Fig. 3 of my lcopending application and the channeling equipment 22 correspondsto and includes one ormore of the filters '5t- Eiland their corresponding converters, 663-14, oscillators SIe-'I5 and filters l@ tor- 84 of fg, 3 of my co-penoling` application.

Another Aportion Ottheoutput of the first dern'odulator I2 is fed throughlines I 4 and I8 to a balanced mixer or detector 2-8. Waves derived from a lo 'calos cillator 2 S operating-at, for example, I I megacycl'es are alsoufedithrough line y2'I to thebalancedmgixer 28. The sum frequency outputofinixer 28 appearing in line 32 is-passed filter andlimiterSll and appears in line-34 as a Wave. having a meanA frequency of 12 megacycles and having allof the'freque'ncy modulation charactr'isticsof the original one megacycle frequency modulated wave appearing in linel I 4.

The 12 megacycle wave having, for example, a maximumsyving of plus and minus 200 kilocycles and appearing in line- 34 is fed intol a second balancedrnixer or 'detector alongk with oscillations derive'dfrom a vsecond local oscillator 50 which may be operating, for example, at a frequency of ISineg'a'cycles Aper second,

"Svvitcliedfto Noscillator'50 by means of-switch 54 is `a reactancetube modulator 5E. fed with 'one or more signaling channels from channeling equipment lill4 and line 58,. Thus three separate voice signals may be fed to the channeling equipment ll through lines B2, 63 and 65. This channeling equipment may correspond, for example, to the channeling equipment associated with channels B, C and D of Fig, l of my co-pending application, provided these channels are not used on the incoming sub-carrier in line I4. In other Words, the -inputin 62, t3 and t5 separately modulate local oscillators such as IDB, EDC, and IOD of Fig. l of my co-pending application operating `at diierent frequencies. Side bands of the resulting modulation are ltered olf by filters such as fIfdB, ICl and IIID of said Fig. 1 and combined and fed into line 58 of Fig. l herein. Obviously, of course, oneof the-channels such as 62 of Fig. 1 maybe fed through-'directly to the reactance tube modulator E as was done in channel A of Fig. 1 of my co-.pending application, providing this channel is not 4already in use on the incoming sub-'carrier in line I4.

As a result, the output of oscillator is frequencymodulatedV by the output of the channel equipment. B and the frequency modulated Wave which appears in line '52 is combined with. the frequency modulated Wave appearing in line 3'4 in the Amixer or detector .36. Of -theresulting waveslilter 38 maybe designed so as -topassthe dile'rence frequency and,. assuming a maximum frequency deviation of v5() kilocycles imparted v-to oscillator 5t by the signals in line 58,'the-o1`1tpu-I of 3B, Which'may, of course, 'includeva vacuum tube limiter if desired, will be a wave havinga mean frequency of one megacycle and .a mauirnumfr'equency Vswing or frequency modulation of 'plus and 'minus-'250 kilocycles. The-latter will truly'represent 'all of the signaling vchannels appearing'inline lll'and also the additional chanlnels injected by 1ine'58 carrying signal channels on bands derived from channeling equipment 6D. The output of'ltr iand'limiter 38 isfthen fed through line #l0 to atransmitter. corresponding 'in "design 'and construction tofther 'frequency modulated oscillator 21| lofFig,` 2 of my copending application. Transmitter 4'2, may thus,for example, be operated at a -mean 4frequency of 3 01'0 megacycles'and the input fed throughline '4t adjusted `s"o as' to 'produce la maximum .deviation of plus and minus one megacycle inV the wave radiated by radiating-antenna'd. The construction of re-radiating lantenna I8 and its reflector E16 together "with connecting transmission vline lili `may beidntical to that shown in Fig. -1`0fof my c'o-pending "application If desiredof'course, switch 54 maybe opened and channeling equipment 'I2 'corresponding to channeling equipment 611- Amay be Vused to-frequency modulate the nrst beating *oscillator 26.. In that 'event switch 66 would be closed, `a.suit ablenlunbler'of'inputs would be provided atM andthe combinedchannels in line-A would be 'used to operate la reactance tube modulator 68. tAlso, Vif dsiredboth switches andE'dwrn-ay be closed'one-or more signals may be `impressed upon "oscillator'Z-'and one or more signalsconcurrently may be impressed upon -oscilllatorfl As shown in Fig. 2 the sameA resultant-modulating voltage may be used 'to simultaneously frequeneyfmoduiate both oscillators zalamiisa. In this 'casa'howeven'the-phase of the resultant voltage applied toltlie reactance tubemodulato-rs lfandV 56r must be opposite so that the total frequency swingrof Vthe oscillatorskisthe sum offrequency-swings'imparted to them.

-Morel'specifically -as shown in Fig.:=2', oscillator 27S- is Aprovidedwithi aa frequency controlling paralle l-'tuned circuit -ll and oscillator'is;providd Y with a parallel tuned `frequency controlling cir-l cuit 82. `The output of channeling equipment 60, through .the action of transformer 80' applies the resultant modulating potentials oppositely to the control :grids of the reactance tubes 55 `and 08 through chokes 80 and88. The valves of frequency swing and mean frequency show-n on Fig. 2 are illustrative only and are not to be considered in any way as restrictive ofthe present invention. l

As in connection with Fig. 1 rectangle 38 may not only represent a lter network but also a vacuum tube limiter. This islalso true of the apparatus represented by rectangle 30.

It should accordingly be clear that whatever frequency modulation exists in line le of either Fig. l'o-r Fig. 2 is also completely present in line 00. In addition, as before explained, line l0 also contains the modulation due to the channels which are locally introduced through equipment 50"provided .at the relaying point. Since the modulationcappearing in line l is not subjected to complete demodulation so as to reproduce the ultimate or elemental signals, cross talk due to unlinearity of discriminators and modulators is not added to the straight through channelsthat is, those received upon the receiving antenna system 2, sand retransmitted over the retransmitting antenna arrangement 4E, ri-even though several channels are added to the through wave at the relaying point as explained.

.My invention is not, of course, restricted to a doubly modulated system such as referred to. For example, the addition of channels to a relay system employing single frequency modul-ation may be accomplished in a similar way. vThus, for" example, assume that the received wavehas amean frequency of 3000 megacycles and has been directly frequency modulated with an audio channel covering a :band of frequencies from 16 cycles to 16,000 cycles and so that the maxim-urn deviation in the received 3000 megacycle Wave is plus and minus 2.5 megacycles. This wave i-s received at the relaying point and beat in apparatus 8 to an intermediate frequency of, for example, 30 megacycles $2.5 megacycles. This 30 me'gacycle` wave may then be heat to a lowfrequency-by oscillator 25 su-ch as, for example, l5 megacycles and then ibeat black up to a higher frequency such as to 60 megacycles with the second oscillator 50. `In this case either or both oscillators as explained in connection with Figs. 1` and Zmay be frequency modulated with one ormore new and different signals introduced at the relaying point. l

A frequency multiplier 400 may be inserted in line 40 before transmitter 42 and following filter and limiter 38. The effect of this multiplier will be to increase the mean frequency of common subcarrier and also its frequency deviation by the multiplying factor, prior to use, for modulation in thefrequency modulated oscillator 42.

The balanced mixers 28 and 3E of Figs. 1 and 2 are preferably of the type sho-wn in Fig. 9 of my (3o-pending application involving the mixer tubes 904, 906, oscillator tube 908 and their yassoelated circuits.

The reactance tubes 56, 68 may, of course, be

lators 26 and 50 respectively. Resistors |04, |06

are'of relatively low value. In this Wayefective quadrature voltage derived from the tuned cir-1 cuits 3i),` v82 is impressed across the and cathodes of `tubes 68, 56. l n i These tubes as connected in Fig. 2 will present a `variable capacitive` :reactance in shunt to the tunedwcircuits 80, 82' which may effectively be grounded at'their lower terminals for high frequency currents by` large bypassing Condensers |08,\||0. 1i 1,

The positions of Condensers |00, |ll2and resistors |04, .|05 may be reversed, in which case the resistors should be blocked oil fromthe plates byseries .connected bypassing `Condensers of large value so as to prevent the plate voltage from control grids' being applied to the grids While allowing A. C.l

components to reach the grids. Alsoin this case the resistorsshould be large in value and the Condensers |00.' |02 vwhen connected between the grids and filaments should be of large capacity or relatively low capacitive reactance. With the latter connections, tubes 06, B8 then` act as variableinductances inshunt to the tuned circuits 80, 82.` l t l Having thus described my invention, what I claim is: l

l. The' method which includes receiving` amultiply modulated wave, subjecting the wave to a Ysingle demodulation, derived from the demodulated wave with signal modulated oscillations,` ltering waves resulting from the heterodyning process, and transmitting theltered waves.

2. The method ofwave conversion which includes subjecting a doubly frequency modulated wave to a single frequency demodulaticn, heterodyning waves ,derived from'the demodulated wave with frequency modulated'oscillations, and transmitting waves resulting from the heterodyning process. Y y 3. The method which includes subjecting a-successivelyY angle modulated wave; to an angle demodulation process, heterodyning Waves de# rived from the dernodulation with an angle modulated oscillation, and transmitting waves derived from the heterodyning process.

4. The method of adding signal channels to a signal carrying, successively angle modulated wave which includes subjecting the waveto an angle demodulation, l generating waves, angle modulating the generated waves` with `Waves representing one or more signal channels, hetero-` dyning waves derived from the demodulation with said waves which have been angle modulated with one or more signal channels which are to be added, and transmitting waves resulting from the heterodyning process,

5. The method of relaying a signal carrying, doubly modulated wave and adding one'or more signal channels to the wave to be relayed which includes subjecting the doubly modulated wave to a, single demodulation, heterodynin-g waves de rived from the demodulation with a wave which has been modulated with one or more signaling channels to be added, ltering the heterodyned waves, generating a high frequency carrier, and modulating the high frequency carrier with the filtered waves.

6. The method of relaying a signal carrying,

doubly angle modulated wave and addingone` or# more signal channels to the Wave tobe relayed which includes subjecting the doubly angle modulated wave to a single angle demodulation, heterodyning the waves derived from the angle demodulation with a wave which has been angle modulated with one'or more signaling channels to be heterodyning i Waves 7 added,` filtering the. heterodyned waves, generating' a high frequency carrier, and angle modulating the hi-gh frequencyv carrier with the filtered Waves.

7. The method of relaying a signal carrying, doubly frequency modulated Wave and adding. one or more signal channels to the Wave to be relayed which includes subjecting the doubly frequency modulated wave to a single frequency demodulation, heterodyning the waves derived from the frequency demodulatlon with awave which has been frequency modulated with one or more signaling channels to be added, filtering the heterodyried waves, generating a high frequency carrier, and frequency modulating the high frequency carrier with the filtered waves.

8. The method of relaying which includes receiving a signal carrying, doubly frequency modulated Wave; subjecting the receivedrvvave to a singlefrequency demodu-lation, heterodyning the demodulated wave to an intermediate frequency, filtering the intermediate frequency wave, heterodyning the filtered wave with an oscillation which has been frequency modulated with bands of frequencies representing one or more signal channels, generating a high frequency carrier, and frequency modulating the high frequency carrier with waves derived from the last-mentioned heterodyning process.

9`; The method of relaying which includes receiving a signal carrying, doubly frequency modulated wave; subjecting the received wave to a single frequency demodulation, heterodyning waves derived from the demodulation with an oscillation which has been frequency modulated with one or more signal channels, filtering out ka band of Waves from the' band of heterodyned Waves, heterodyning the filtered Waves to occupying a different position in the frequenl7 Spectrum, generating a high frequency carrier, and frequency modulating the generated carrier with the heterodyned band occupying said different position.

l0. The method of relaying which includes receiving a signal carrying, doubly frequency modulated wave; subjecting the received Wave to a single frequency demodulation, successively heterodyning the demodulated waves with two locally Ygenerated oscillations, oppositely frequency modulating the locally generated oscillations 4with bands of frequencies representing one or more signaling channels, generating a high frea quency carrier, and frequency modulating the high frequency carrier with waves derived from the'seoond heterodyning process.

11. Relaying apparatus comprising means for receiving a signal carrying, doubly frequency modulated wave,. a discriminator-detector circuit for subjecting the received waves to a Single frequency demodulation, a pair of generators for generating two high, frequency oscillations, means for successively heterodyning the demodulated waves with waves from the two generators, circuits for oppositely frequency modulating the two generated oscillations with waves representing one or more signaling channels, means for generating a high frequency carrier, and means for frequency modulating the high frequency carrier with Vwaves derived from the second heterodyning process.y

12. Relaying apparatusl including means for receiving a signal carrying, doubly frequency modulated wave, a discriminator-detector circuitI for subjecting the received Iwave to a single frequency demodulation, means for'heterodyning waves derived from the demodulation with an oscillation which has been frequency modulated with one or more signal channels, a filter for filtering a band of waves fromrthe heterodyned waves, apparatus for heterodyning the filtered band of Waves to waves having different meanfrequency than said filtered band, a generator for generating a high frequency carrier, and circuits operating to frequency modulate the generated carrier With the heterodyned waves of kdifferent mean frequency.

13'. Relaying apparatus including means for receiving a signal carrying, doubly frequency modulated wave, a demodulator system forv subjecting the received wave to a single frequency demodulation, means for heterodyning the demodulated Wave to anintermediate frequency, a filter filtering the intermediate frequencyY wave, means for heterodyning the filtered wave with an oscillation which has been frequencymodulated with waves representing one or more signal channels, means for generating a high frequency carrier, and means for frequency modulating the high frequency carrier with waves derived from the last-mentioned heterodyning process.

14. Means for relaying a signal carrying, doubly frequency modulated wave and adding one or more signal channels to the wave to be relayed which includes means for subjecting the doubly frequency modulated wave to a single frequency demodulation, means for heterodyning the Waves derived from the frequency demodulation with a- Wave which has been frequency modulated with waves representing one or more signaling channels to be added; means for filtering and limiting the heterodyned Waves, means for generating a high frequency carrier, and means for frequency modulating the high frequency carrier with the limited and filtered waves.

15V. Apparatus for relaying a signal carrying, doubly angle modulated wave and adding one or more signal channels to the wave to be relayed which includes demodulating apparatus operating to subject the doubly angle modulated Wave to a single angle demodulation, a mixer for heterodyning the waves derived from the angle demodulation with a wave which has been angle modulated with Wavesrepresenting one or more signaling channels to be added, a filter filtering the heterodyned Waves, an oscillator generating a high frequency carrier, and a modulator for angle modulating the high frequency carrier with the filtered waves. Y

16. Apparatus for relaying a signal carrying, doubly modulated wave and adding one or more signal channels to the wave to be relayed compri-sing a-demodulator for subjecting the doubly modulated wave to a single demodulation, a mixer for heterodyning the waves derived from the demodulationwitha signal modulated Wave, a filter Afor filtering the heterodyned Waves, a generator for generating a high frequency carrier, and a circuit for modulating theV high frequency carrier with the filtered Waves.

17. Apparatus for adding signal channels to a successively angle modulated wave comprising a demodulator for subjecting the wave to an angle demodulation, a mixer for heterodyning Waves derived from the demodulation with a wave which has been angle modulated with waves representing one or more signal channels which are to be added, filtering and limiting apparatus to filter and limit the ,output of saidV mixer and means for utilizing the filtered and'limited'waves.

tion, modulated in accordance with waves representing one or more bands of frequencies, and means for utilizing the Waves resulting from the heterodyning process.

20. In combination, means for receiving a multiply modulated Wave, a demodulator for subjecting the wave to a single demodulation, a mixer for heterodyning the demodulated Iwave with an oscillation which has been modulated with waves representing one or more bands of frequencies, and a circuit utilizing the wave resulting from the heterodyning process.

LELAND E. THOMPSON. 

